From what I can see they're exactly the same plugin, just wondered what the difference is here? Seems strange that two different developers both have their own emulation?
There's also the SSL plugins that both developers have done, I'm sure there's a couple others as well
From what I know the UAD plugins are the absolute bees knees and are so close to the real hardware it's scary... then again... I'm pretty sure this is the case for a lot of the Waves bits as well and neither come cheap...??
They're better because they can call on more DSP due to the additional processing power the UAD stuff comes with. So the emulsions might go into more depth than any of standard ones that don't have their own CPU so to speak.
And from what I've heard from a lot of different people I trust who've A/B the real hardware with the plug ins. There's virtually no difference on a blind test - like you struggle to tell which one is better.